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1. All-normal dispersion fiber laser with a bandwidth tunable fiber-based spectral filter

   https://doi.org/10.1364/OL.398049  

   Khanolkar, Ankita; Ge, Xiaowei; Chong, Andy (August 2020, Optics Letters)

   We investigate numerically and experimentally an all-fiber, bandwidth tunable spectral filter comprising birefringent fibers. The spectral bandwidth tunability of the filter is based on the compensation of birefringence in polarization maintaining fibers. This unique filter allows mode-locked operation of a fiber oscillator with the ability to generate distinct laser modes with different output spectral shapes and pulse evolutions. 

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2. Complex Swift Hohenberg Equation (CSHE) Dissipative Soliton Fiber Laser

   Khanolka, A; Zang, Y; Chong, A (January 2021, Conference on Lasers and Electrooptics)

   null (Ed.)

   We report dissipative solitons of CSHE in a mode-locked fiber laser by employing a unique fiber filter which produces a fourth order spectral response. The laser generates moving, asymmetric pulses with a highly asymmetric spectrum. 

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3. Ultrabroadband, few-cycle pulses directly from a Mamyshev fiber oscillator

   https://doi.org/10.1364/PRJ.8.000065  

   Ma, Chunyang; Khanolkar, Ankita; Zang, Yimin; Chong, Andy (December 2019, Photonics Research)

   While the performance of mode-locked fiber lasers has been improved significantly, the limited gain bandwidth restricts them from generating ultrashort pulses approaching a few cycles or even shorter. Here we present a novel method to achieve few-cycle pulses ( $\sim 5\text{cycles}$) with an ultrabroad spectrum ( $\sim 400\mathrm{nm}$at $-20\mathrm{dB}$) from a Mamyshev oscillator configuration by inserting a highly nonlinear photonic crystal fiber and a dispersion delay line into the cavity. A dramatic intracavity spectral broadening can be stabilized by the unique nonlinear processes of a self-similar evolution as a nonlinear attractor in the gain fiber and a “perfect” saturable absorber action of the Mamyshev oscillator. To the best of our knowledge, this is the shortest pulse width and broadest spectrum directly generated from a fiber laser. 

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4. Complex Swift Hohenberg equation dissipative soliton fiber laser

   https://doi.org/10.1364/PRJ.419686  

   Khanolkar, Ankita; Zang, Yimin; Chong, Andy (May 2021, Photonics Research)

   Complex Swift Hohenberg equation (CSHE) has attracted intensive research interest over the years, as it enables realistic modeling of mode-locked lasers with saturable absorbers by adding a fourth-order term to the spectral response. Many researchers have reported a variety of numerical solutions of CSHE which reveal interesting pulse patterns and structures. In this work, we have demonstrated a CSHE dissipative soliton fiber laser experimentally using a unique spectral filter with a complicated transmission profile. The behavior and performance of the laser agree qualitatively with the numerical simulations based on CSHE. Our findings bring insight into dissipative soliton dynamics and make our mode-locked laser a powerful testbed for observing dissipative solitons of CSHE, which may open a new course in ultrafast fiber laser research. 

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5. Microcombs in fiber Fabry–Pérot cavities

   https://doi.org/10.1063/5.0177134  

   Musgrave, Jonathan; Huang, Shu-Wei; Nie, Mingming (December 2023, APL Photonics)

   Optical frequency combs, which consist of precisely controlled spectral lines covering a wide range, have played a crucial role in enabling numerous scientific advancements. Beyond the conventional approach that relies on mode-locked lasers, microcombs generated from microresonators pumped at a single frequency have arguably given rise to a new field within cavity nonlinear photonics, which has led to a robust exchange of ideas and research between theoretical, experimental, and technological aspects. Microcombs are extremely attractive in applications requiring a compact footprint, low cost, good energy efficiency, large comb spacing, and access to nonconventional spectral regions. The recently arising microcombs based on fiber Fabry–Pérot microresonators provide unique opportunities for ultralow noise and high-dimensional nonlinear optics. In this review, we comprehensively examine the recent progress of fiber Kerr microcombs and discuss how various phenomena in fibers can be utilized to enhance the microcomb performances that benefit a plethora of applications. 

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